JEE Main 2024 — Biomolecules Question with Solution

The ninhydrin test is a chemical test which is used to detect the presence of amino acids or proteins. When amino acids or proteins react with ninhydrin, a deep blue or purple color is produced, which is indicative of a positive test. This reaction primarily occurs due to the reaction of ninhydrin with the free amino groups (-NH₂) present in amino acids or proteins.

Let's examine each option:

Option A: Polyvinyl chloride - Polyvinyl chloride, commonly known as PVC, is a synthetic polymer. It does not contain amino acids or free amino groups. Therefore, it does not give a positive test with ninhydrin.

Option B: Cellulose - Cellulose is a carbohydrate polymer consisting of glucose units. It is the main constituent of the cell wall in plants. Like PVC, cellulose does not contain amino acids or free amino groups, so it also does not give a positive test with ninhydrin.

Option C: Egg albumin - Egg albumin is a protein found in egg whites. Proteins are made up of amino acids linked by peptide bonds, and free amino groups are present in the structure of proteins. Therefore, egg albumin reacts with ninhydrin and gives a positive test by producing a deep blue or purple color.

Option D: Starch - Starch is a polysaccharide composed of glucose units and is a carbohydrate like cellulose. It does not possess amino acids or free amino groups. Consequently, starch does not give a positive test with ninhydrin.

Based on the explanation, the correct answer is Option C: Egg albumin, as it is the only option among the ones listed that contains proteins, which have free amino groups capable of reacting with ninhydrin to give a positive test.